Adjustable damping arrangement for a non-rotating tool holder

ABSTRACT

A damper assembly for use with a non-rotating tool holder includes a hollow ram for supporting a non-rotating tool and a damper assembly mounted in the hollow ram for absorbing vibrations of the ram. The damper assembly includes a front plate and a rear plate, an upper tie rod and a lower tie rod extending between the front plate and the rear plate, and a damper mass mounted between the front plate and the rear plate. Ring dampers are mounted between the damper mass and the front and rear plates, and suspension springs are mounted between the upper tie rod and the lower tie rod. The suspension springs carry the weight of the damper mass so that the ring dampers do not have to carry the weight of the damper mass, and the damper mass is free to respond to vibrations in the ram.

FIELD

An adjustable damping arrangement for a non-rotating tool holder usessprings to suspend a damper mass in the interior of the ram and dampingrubber rings that can be selectively compressed to adjust the dynamicstiffness of the ram.

BACKGROUND

Lathe cutting capability is limited by the dynamic stiffness of themachine tool structure. Cutting tools supported by narrow rams at longextensions on vertical lathes provide the reach to cut tall parts, butoften lack adequate stiffness. The value of dynamic stiffness varieswith frequency and is lowest at specific frequencies related tostructural natural frequencies or modes. The minimum stiffness can be50% or less than the stiffness at the rest of the frequencies, anddefines the cutting capacity of the machine. The frequency, stiffness,modal mass, and damping can vary as the machine elements are moved overtheir operating ranges.

The critical characteristics of dynamic stiffness are static stiffness,mass, and damping. Static stiffness and mass are often dictated by themachine type and size and can be difficult to alter significantly.Damping which may be defined as the ability to absorb or neutralizevibrating energy can be increased through the addition of machineelements. Greater damping results in higher stiffness.

Adding a damper to the ram near the cutting tool will increase thecutting capacity of a vertical lathe. A spring-mass-damper may be tunedto a particular frequency for operation of the ram at the greatestextension, the lowest stiffness condition for the ram.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a ram with a cutting tool attached.

FIG. 2 is a side sectional view of a ram showing a mass damper installedin the interior of the ram.

FIG. 3 is a perspective view of the tie rods and the suspension springsused in a damper assembly.

FIG. 4 is a perspective view of the tie rods connected to the frontplate of a damper assembly and mounted on a tool holder.

FIG. 5 is a perspective view of the tie rods, the tension rod, and thesuspension springs of a damper assembly.

FIG. 6 is a perspective view of the tie rods, the tension rod, and thesuspension springs attached to the front plate of a damper assembly.

FIG. 7 is a perspective view of a damper assembly mounted on a toolholder.

FIG. 8 is a side sectional view of a damper assembly.

FIG. 9 is a bottom view of the damper assembly showing the suspensionfor the damper mass.

FIG. 10 is a perspective view of the damper assembly.

FIG. 11 is a perspective view of the rear plate of the damper assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a perspective view of a ram generally designated by thereference numeral 10. The ram 10 may be used on a lathe and comprises ahollow beam 12 having an interior wall 13 best seen in FIG. 2. A cuttingtool holder 14 may be mounted on the front end 16 of the ram 10 whichmay support one or more cutting tools 18. Although two tools 18 areshown in the drawing, only one tool at a time is used in a cuttingoperation. The ram may move vertically or horizontally during operation,but the ram 10 and the tools 18 do not rotate.

FIG. 2 is a side sectional view of a ram 10 showing a damper assembly 21having a damper mass 20 installed in the interior of the ram 10. Thedamper mass 20 may be mounted between a front plate 22 and a rear plate24 in the interior of the hollow beam 12. Upper and lower tie rods 25and 26, respectively, pass through the front plate 22, the damper mass20, and the rear plate 24. Ring dampers in the form of stiff rubberrings 30 best seen in FIGS. 4, 5, and 6 are positioned between thedamper mass 20 and the front and rear plates 22 and 24, respectively. Asshown on FIGS. 3 and 8, tie rod nuts 27 may be used on the threaded ends28 of the tie rods 25 and 26 to fix the distance between the front plate22 and the rear plate 24.

As shown on FIGS. 6, 8, and 10, the ends of the tie rods 25 and 26 passthrough a tie rod mounting block 32 that is positioned on an end bracket23 that is mounted on the front plate 22. A tuning bolt 64 may bethreaded into a tuning block 29 and may be mounted on the tie rodmounting block 32 by bolts 54. The end of the tuning bolt 64 abuts atuning bolt spacer 65. A slotted disk 60 may be positioned between theend bracket 23 and the front plate 22, and the slotted disk 60 may beformed with a hex shaped center aperture 31 which engages a hex head end41 on a tension rod 40. The slots 61 in the disk 60 may be engaged by adisk locking bolt (not shown) to prevent the disk 60 from rotating asexplained more fully below.

As shown on FIGS. 3-6 suspension springs 34 may be used to support thedamper mass 20 from the upper tie rod 25. The suspension springs 34 maybe hung from suspension brackets 35 which rest on the upper tie rod 25.The suspension springs 34 pass through vertical bores 36 in the dampermass 20 (best seen in FIGS. 2 and 3) and hook onto support pins 37 whichengage the bottom surface 38 of the damper mass 20. Eight suspensionsprings 34 are shown supporting the damper mass 20, four near the frontplate 22 and four near the rear plate 24, but a fewer or a greaternumber of suspension springs may be used.

As shown in FIG. 8, the tension rod 40 passes through the center of thedamper mass 20 and is threaded into a plug 42 having a cam surface 43mounted in a bore in the rear plate 24. The cam surface 43 engages afollower surface 46 on a locking lever 47 as shown on FIGS. 7, 8 and 11.As shown in FIG. 7, the locking lever 47 has two locking feet 48 whichare positioned near the outer periphery of the rear plate 24. Movementof the cam surface 43 toward the damper mass 20 causes the locking lever47 to move radially outward toward periphery of the rear plate 24.

As shown in FIG. 9, the support pins 37 may be threaded through the endsof the suspension springs 34 to support the bottom surface 38 of thedamper mass 20. Thus, the upper and lower tie rods 25 and 26,respectively, do not have to squeeze the stiff rubber rings 30 withenough force to support the weight of the damper mass 20. The suspensionsprings 34 provide sufficient freedom of movement to the damper mass 20so that it is able to damp the vibrations in the ram 10.

As shown in FIG. 10, the front plate 22 may have two locking pistons 51positioned near the outer periphery of the front plate 22. The pistons51 are actuated by bolts 66 which have a cam surface 67. FIG. 8 showsthe cam surface 67 on one of the bolts 66 that is used to force thelocking piston 51 outward as the bolt 66 draws the cam surface 67against the locking piston 51.

In order to install the damper into the ram, the following procedure maybe used. The damper assembly 21 may be inserted into the interior of theram 10 and the front plate 22 rests against the interior wall 13. Bolts66 may then be tightened forcing the cam 69 to move the locking pistons51 outward to secure the front plate 22 against the interior wall 13 ofthe ram. Next the tension rod 40 may be tightened (which also rotatesthe slotted disk 60) to draw the plug 42 into the bore in the rear plate24 to force the locking lever 47 and the locking feet 48 against theinterior wall 13 of the ram. The tension rod 40 is only tightened enoughto remove any looseness in the fit of the damper assembly 21 in the boreof the hollow beam 12 and provide light contact pressure against theinterior wall 13 of the ram. At this point in the installation, the rearplate 24 will be snug in the ram bore yet will be able to slide axiallywhen the rubber rings 30 are compressed. To prevent the tension rod 40from vibrating loose, a locking bolt (not shown) may be inserted intoone of the slots 61 in the slotted disk 60 and threaded into the frontplate 22 to prevent rotation of the disk 60 and loosening of the tensionrod 40. The slots 61 in the disk 60 may be spaced differently from thethreaded openings in the front plate 22 that receives the locking bolt.This difference operates as a Vernier and allows the disk 60 to belocated at increments that are smaller than the spacing between adjacentslots 61.

The upper and lower tie rods 25 and 26 exert pressure on the stack ofparts consisting of the rear plate 24, the rear rubber rings 30, thedamper mass 20, the front rubber rings 30, the front plate 22, the endbracket 23 and the tie rod mounting block 32. The tie rod nuts 27 on theupper and lower tie rods 25 and 26 are set to the length of thecomponents with no pressure on the rubber rings 30. In this adjustment,the rubber rings 30 are in their loosest state, and the damper frequencyis low.

The dynamic stiffness of the ram may be adjusted by tuning the dampermass 20 to a particular frequency. The resonant frequency of the dampermass 20 may be adjusted to the resonant frequency of the ram bycompressing the rubber rings 30.

In order to compress the rubber rings 30, the tuning bolt 64 is used.The tuning bolt 64 is threaded into the tuning block 29, and the end ofthe tuning bolt 64 abuts the tuning bolt spacer 65. Turning the tuningbolt 64 advances it into the tuning block 29 and presses onto the tuningbolt spacer 65, the slotted disc 60, and the front plate 22 to increasethe compression on the rubber rings 30.

In use, the locking feet 48 mechanically couple the rear plate 24 to theinterior wall 13 of the ram 10, and the locking pistons 51 couple frontplate to the interior wall 13 of the ram 10. The front plate 22 and therear plate 24 transfer vibration of the ram 10 to the rubber rings 30which react against the damper mass 20 to absorb vibrational energy ofthe ram. Because the suspension springs 34 support the weight of thedamper mass 20, and the upper and lower tie rods 25 and 26 do not haveto squeeze the stiff rubber rings 30 with enough force to support theweight of the damper mass 20, the damper mass 20 has sufficient freedomof movement so that it is able to damp the vibrations in the ram 10.

Having thus described the device, various modifications and alterationswill occur to those skilled in the art, which modifications andalterations are intended to be within the scope of the device as definedby the appended claims.

1. A damper assembly for use with a non-rotating tool holder, the damperassembly comprising: a hollow ram for supporting a non-rotating tool; adamper assembly mounted in the hollow ram for absorbing vibrations ofthe hollow ram, the damper assembly comprising; a front plate and a rearplate mounted in the hollow ram; an upper tie rod and a lower tie rodextending between the front plate and the rear plate; a damper massmounted between the front plate and the rear plate; ring dampers mountedbetween the damper mass and the front and rear plates; suspensionsprings mounted between the upper tie rod and the lower tie rod, thesuspension springs carrying the weight of the damper mass, whereby thering dampers do not carry the weight of the damper mass and the dampermass is free to respond to vibrations in the ram.
 2. The damper assemblyof claim 1 further comprising: at least one locking foot mounted on therear plate; a tension rod extending between the front plate and the rearplate and passing through the damper mass, whereby the tension rodextends the at least one locking foot to mechanically couple the rearplate to the interior of the hollow ram.
 3. The damper assembly of claim2 further comprising: a locking lever mounted on the rear plate; a plugmounted in the rear plate and engaged with the tension rod; a camsurface on the plug and a follower surface on the locking lever engagedwith the cam surface on the plug, whereby the tension rod may betightened to force the cam surface of the plug against the followersurface on the locking lever to extend the at least one locking foot onthe locking lever into engagement with the interior wall of the hollowram.
 4. The damper assembly of claim 3 further comprising: at least onepiston mounted on the front plate; and at least one actuating bolt onthe front plate with a cam surface in engagement with the at least onepiston, whereby the actuating bolt may be used to extend the at leastone piston into engagement with the interior wall of the hollow ram. 5.The damper assembly of claim 4 further comprising: a slotted diskmounted on the front plate, the slotted disk being coupled to thetension rod, whereby rotation of the tension rod causes a rotation ofthe slotted disk, and wherein the slotted disk may be locked againstrotation to prevent rotation of the tension rod.
 6. The damper assemblyof claim 1 further comprising: a cutting tool holder mounted on an endof the hollow ram; at least one cutting tool mounted on the cutting toolholder, wherein the damper assembly is mounted in the hollow ram in thesame end of the hollow ram as the cutting tool holder.
 7. The damperassembly of claim 6 further comprising: two cutting tools mounted on thecutting tool holder.
 8. The damper assembly of claim 1 furthercomprising: vertical bores formed in the damper mass; and, support pinsengaging the bottom surface of the damper mass, wherein the suspensionsprings pass through the vertical bores and the support pins arethreaded through the ends of the suspension springs to support thedamper mass.
 9. The damper assembly of claim 8 further comprising: twovertical bores formed in the damper mass; and, at least four suspensionsprings comprising the suspension springs, wherein the at least foursuspension springs are divided equally between the two vertical bores.10. The damper assembly of claim 9 further comprising: eight suspensionsprings comprising the suspension springs, wherein four suspensionsprings are positioned in a first vertical bore and four suspensionsprings are positioned in a second vertical bore.
 11. The damperassembly of claim 3 wherein the tension rod is tightened to draw a pluginto a bore and to extend a locking lever against the interior wall ofthe ram, whereby a light contact pressure is provided against theinterior inner wall of the ram and the rear plate will be snug in theram bore.
 12. The damper assembly of claim 7 wherein only one tool at atime is used in a cutting operation.
 13. The damper assembly of claim 8wherein the damper assembly is used in a non-rotating operation and thevertical bores remain in a vertical orientation during the use of thehollow ram and the least one tool.
 14. The damper assembly of claim 1further comprising: rubber rings comprising the ring dampers.
 15. Thedamper assembly of claim 3 further comprising: two locking feet formedon either end of the locking lever, whereby the locking feet engage theinterior wall of the hollow beam near the outer periphery of the rearplate.
 16. The damper assembly of claim 1 further comprising: twopistons mounted on the front plate, whereby the two pistons are mountedat spaced locations near the outer periphery of the front plate, andwhereby the two pistons are movable outward to engage the interior wallof the ram.